Double-heterostructure diode lasers based upon epitaxial layers of GaInAsP grown upon InP substrates have been disclosed. See Bogatov, A. P., Dolginov, L. M., Druzhinina, L. V., Eliseev, P. G., Sverdlov, B. N., and Schevchenko, E. G., Sov. J. Quantum Electron., 4, 1281 (1975); Hsieh, J. J., Appl. Phys. Lett., 28, 283 (1976); and Pearsall, T. P., Miller, B. I., Capik, R. J. and Bachman, K. J., Appl. Phys. Lett., 28, 499 (1976). The emission wavelength of such lasers can be controlled within the range of about 0.95-1.70 .mu.m at room temperature without significantly detracting from good lattice-matching by simply changing the composition of the quaternary solid solution of GaInAsP. Since this range includes 1.1-1.3 .mu.m, the region currently thought to be optimum for optical communication systems utilizing fused silica fibers, these lasers are prime candidates for use in optical communications.
In order for such lasers to be utilized in optical communication systems, nevertheless, detector systems capable of operating within this wavelength range will also be necessary. In particular, it would be advantageous to have an avalanche photodiode capable of operating within this wavelength range.
Photodiodes fabricated from silicon and germanium have been known for many years. Silicon, however, has a low quantum efficiency for wavelengths longer than 1.1 .mu.m. Germanium, on the other hand, has nearly equal ionization coefficients for electrons and holes, which leads to a large excess noise factor and inherently lower speed of response. Germanium also has a smaller than optimum bandgap for 1.3 .mu.m peak wavelength response which results in a large dark current unless cooled below room temperature.
More recently, avalanche photodiodes have been fabricated from materials including GaInAs and GaAsSb epitaxially grown on GaAs substrates. In these systems, severe lattice-mismatches between the epitaxial layer and the GaAs substrate have necessitated intermediate matching layers of other compositions. This has necessitated complicated and delicate structures which require elaborate fabrication procedures. Additionally, yields of reasonably performing devices have been very low. Furthermore, most of the work done in regard to detectors with these systems have resulted in detectors which respond only out to wavelengths of about 1.1 .mu.m. The lattice-mismatch problems become much more severe for compositions capable of responding to longer wavelengths.
Avalanche photodiodes have also been fabricated from the ternary alloy GaInAs grown lattice-matched to InP substrates. See Pearsall, T. P. and Hopson, Jr., R. W., J. Electron. Mater., 7, 133 (1978). Although avalanche gain was noted at 1.2 .mu.m, the peak response with this system was fixed at about 1.6 .mu.m and could not to be chosen to optically respond to any particular desired wavelength. Further, the single heterostructure design led to the loss of photogenerated carriers by surface recombination, leading to reduced quantum efficiency.
Even more recently, avalanche photodiodes have been fabricated employing the quaternary GaInAsP on InP substrates. See Hurwitz, C. E. and Hsieh, J. J., "Topical Meeting on Integrated and Guidewave Optics", Digest of Technical Papers presented Jan. 16-18, 1977, pages MCl-1, 2 and 3 (1978).